Adjustable tread axle assemblies are used in many agricultural devices for setting wheel spacing to accommodate a particular row spacing, implement configuration or the like. For example, in some harvesters and self-propelled field sprayers, a long casting includes a knee joint at one end which supports a king pin assembly. The opposite end of the casting is slidably received within a tube fixed to the sprayer frame. One problem with such an assembly is the high cost for machining the long casting. Also, machining a full casting may be limited because of the machine bed size and travel or machining center requirements for the process. Many knee joints have to be welded so that steel rather than a less expensive ductile iron must be used. Additional machining is required to provide pads on the casting which contact shims necessary to reduce looseness between the casting and the receiving tube. Often, the left-hand and right-hand assemblies have to be separately manufactured with few if any common parts, adding to the expense and the number of parts required.